Genomic Screening for Pathogenic Transthyretin Variants Finds Evidence of Underdiagnosed Amyloid Cardiomyopathy From Health Records

Background New treatments for transthyretin amyloidosis improve survival, but diagnosis remains challenging. Pathogenic or likely pathogenic (P/LP) variants in the transthyretin (TTR) gene are one cause of transthyretin amyloidosis, and genomic screening has been proposed to identify at-risk individuals. However, data on disease features and penetrance are lacking to inform the utility of such population-based genomic screening for TTR. Objectives This study characterized the prevalence of P/LP variants in TTR identified through exome sequencing and the burden of associated disease from electronic health records for individuals with these variants from a large (N = 134,753), primarily European-ancestry cohort. Methods We compared frequencies of common disease features and cardiac imaging findings between individuals with and without P/LP TTR variants. Results We identified 157 of 134,753 (0.12%) individuals with P/LP TTR variants (43% male, median age 52 [Q1-Q3: 37–61] years). Seven P/LP variants accounted for all observations, the majority being V122I (p.V142I; 113, 0.08%). Approximately 60% (n = 91) of individuals with P/LP TTR variants (all V122I) had African ancestry. Diagnoses of amyloidosis were limited (2 of 157 patients), although related heart disease diagnoses, including cardiomyopathy and heart failure, were significantly increased in individuals with P/LP TTR variants who were aged >60 years. Fourteen percent (7 of 49) of individuals aged ≥60 or older with a P/LP TTR variant had heart disease and ventricular septal thickness >1.2 cm, only one of whom was diagnosed with amyloidosis. Conclusions Individuals with P/LP TTR variants identified by genomic screening have increased odds of heart disease after age 60 years, although amyloidosis is likely underdiagnosed without knowledge of the genetic variant.

T ransthyretin amyloidosis (ATTR) encompasses a group of systemic diseases characterized by the extracellular accumulation of insoluble transthyretin (also known as prealbumin) fibrils (1). Although many cases are attributed to agerelated misaggregation of genetically normal ("wildtype") transthyretin, pathogenic or likely pathogenic (P/LP) variants in the transthyretin gene (TTR) are also known to cause protein misfolding, leading to hereditary disease (hATTR) (2). Most commonly, hATTR clinically manifests as polyneuropathy and/or cardiomyopathy, with an estimated prevalence of 1:100,000 in the United States (3). However, this prevalence is likely underestimated due to the challenges of diagnosing patients with hATTRassociated cardiomyopathy and polyneuropathy (4).
The advent of more widespread genetic testing facilitated by next-generation DNA sequencing technologies presents new opportunities to potentially redefine our understanding and approach to hATTR diagnosis and treatment. Identifying individuals at risk through systematic screening for genomic variants in TTR, rather than symptom-based clinical ascertainment, could both clarify the true scope of the disease at a population scale and enable earlier intervention to potentially mitigate disease progression and thereby improve outcomes (5). Because hATTR cardiomyopathy is generally only clinically recognized once profound ventricular remodeling and dysfunction are present these opportunities for improving outcomes may be substantial, particularly in light of newly approved treatments (1,6). In fact, the Clinical Genome Resource Actionability Working Group has recently upgraded its assertion for TTR and cardiac amyloidosis to "strong actionability" (7); however, they do note that there is limited evidence informing disease likelihood and intervention effec- To establish the potential efficacy of this genomefirst approach, it is first important to understand the population prevalence of P/LP variants in TTR and how they present clinically, independent of a symptoms-based ascertainment. For example, Damrauer et al (9) recently showed significantly increased odds of heart failure in genetically ascertained individuals of African ancestry older than the age of 50 years with a specific TTR variant-V122I, also known as p.V142I (9). This variant is common (up to 4%) in individuals of African ancestry, with at least one study finding an incidence of heart failure of 29% over 21.5 years of follow-up (10)(11)(12) Table 2); results are shown in Table 5.      Values are n (%) unless otherwise indicated. OR and P values based on logistic regression model adjusted for age, age 2 , sex, and principal components 1-4 of ancestry; 95% CI and P values based on bootstrapped sampling procedure; Reported P values are adjusted to control false discovery rate. a OR and P values not reported due to limited observations. b Includes gastroparesis, orthostatic hypotension, and eccrine sweat disorder. c Other system denotes any peripheral neuropathy, autonomic neuropathy, ophthalmology, or miscellany.
CI ¼ confidence interval; NA ¼ not available; OR ¼ odds ratio; other abbreviations as in Tables 1 and 4.   showing that V122I was associated with increased odds of heart failure with advanced age (65 years and 50 years, respectively). Our findings were not specific to V122I alone, as later-onset cardiomyopathy was also observed in association with V30M, T60A, and I68L.

ALTERNATIVE
EXPLANATIONS FOR LIMITED DISEASE ASSOCIATIONS. Nonpenetrance is also a factor in explaining our findings. Incomplete (if not low) penetrance has been a consistent finding in numerous genome-first inherited cardiomyopathy studies, so a similar pattern for TTR is possible (26,27). Despite an increased OR, only 12% and 22% of carriers $60 years of age were observed to have cardiomyopathy and heart failure, respectively, in our analysis. These data are consistent with a longitudinal analysis of individuals with V122I from ARIC, which reported 29% incidence of heart failure and fewer than 7% with incidence of hypertrophy and an infiltrative phenotype by echocardiography after 21.5 years of follow-up (12).
Under-recognition of ATTR also likely contributed to the limited associations observed from this retrospective analysis. Unfamiliarity with the diseaseparticularly outside of specialized centers-is known to present challenges to proper diagnosis and treatment (28,29). Patients may present with any number of nonspecific and heterogeneous symptoms, including those that arise from peripheral neuropathy; autonomic neuropathy; heart failure; and  Values are n (%) unless otherwise indicated. OR and P values based on logistic regression model adjusted for age, age 2 , sex, and principal components 1-4 of ancestry. 95% CI and P values based on bootstrapped sampling procedure. Reported P values are adjusted to control false-discovery rate. a OR and P values not reported due to limited observations. b Includes gastroparesis, orthostatic hypotension, and eccrine sweat disorder. c Other system denotes any peripheral neuropathy, autonomic neuropathy, ophthalmology, or miscellany. Tables 1 and 3. dysfunctions of the eye, kidneys, thyroid, adrenal glands, and blood vessels (30,31).       Values are n (%). OR and P values based on logistic regression model adjusted for age, age 2 , sex, and principal components 1-4 of ancestry. 95% CI and P values based on bootstrapped sampling procedure. Reported P values are adjusted to control false-discovery rate. a OR and P values not reported due to limited observations. b Includes gastroparesis, orthostatic hypotension, and eccrine sweat disorder. c Other system denotes any peripheral neuropathy, autonomic neuropathy, ophthalmology, or miscellany. Tables 1 and 3